Figure selection with push buttons



April 19, 1955 1 w. HULLEGARD ETAL 2,706,746

FIGURE SELECTION WITH PUSH BUTTONS Filed July 11, 1951 3 Sheets-Sheet l3 Sheets-Sheet 3 E. w. HULLEGARD ETAL FIGURE SELECTION WITH PUSH BUTTONSR75 R76 R17 19/8 R19 R20 R21 R22 ll as:

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April 19 Filed July 11, 1951 United States Patent FIGURE SELECTION WITHPUSH BUTTONS Erik Waldemar Hullegard, Stockholm, Lars Gunnar Ulin,Malarhojden, and Anders Georg Valentin Larshans, Tallberg, Sweden,assignors to Telefonaktiebolaget g, Pg Ericsson, Stockholm, Sweden, acompany of we en Application July 11, 1951, Serial No. 236,242

Claims priority, application Sweden July 21, 1950 4 Claims. (Cl. 179-16)The present invention relates to such automatic telephone systems, inwhich the subscribers instruments are for the sending of figuresprovided by means of push buttons instead of dials, and besides comprisea tone frequency generator for emission of different tone frequencycurrents depending on which one of the push buttons is pressed down.

The tone frequency currents actuate a tone signal receiver at anexchange and are transmitted to a register, which provides for theconnection to a called line. Each tone signal receiver is suitablyconnected with a register and the so connected units are common to agreat number of subscribers lines. Due to the subscribers lines being ofvarying lengths and having different electrical properties difficultiesthereby arise in separating tone frequency signals by means of filtersand preventing the effect of disturbing voltages.

According to the invention disturbances from harmonies in non-sinusoidalwaves, which are prevented by for at least one of the voice frequencycurrents to be a harmonic at the fundamental frequency for another oneof the voice frequency currents, and by connecting the band pass filtersto allow a harmonic to pass to only one receiving circuit to designate asignal in the receiver, while a band pass filter for a fundamentalfrequency is connected to at least two receiving circuits, one of whichis also connected to the filter for one harmonic corresponding to thefundamental frequency, and which two circuits in combination designate aseparate signal.

An embodiment of the invention will be described more fully below withreference to the accompanying drawings Figs. 1-4.

Fig. 1 shows a subscribers instrument;

Fig. 2 shows on the upper part of the drawing a part of a connectinglink and on the lower part of the drawing a part of the tone signalreceiver in a register comprising a trigger and a device for supplyingthe subscribers instrument with direct current;

Fig. 3 shows relays for the register and filters for the tone signalreceiver in the register; and,

Fig. 4 shows how Figs. l-3 must be assembled.

In Fig. 1, M designates a microphone, H a telephone receiver and T11 atransformer and R a bell connected in series with a condenser C11. Theswitch hook actuates the contacts 11-14, which are shown in their restposition on the drawing. A push button K with contacts 16-16 depends insuch a manner on the switch hook of the instrument, that if the pushbutton is pressed down while the micro-telephone rests on the switchhook it is gifend held by a spring 17 until the micro-telephone is Theinstrument further comprises a tone frequency generator consisting of anelectron tube E1, two transformers T12 and T13, the resistances m11--m14and the condensors C13C14. The frequency developed by the generator canbe varied by means of push buttons Pl-Plt) and a condenser C15.

The subscribers line a--b is connected to a telephone exchange and uponoriginating a call is connected over a line finder SaCc in Fig. 2 to aconnecting link SN, which is connected to a register REG by means of aregister finder VaVc.

The electron tube E21 and the discharge lamp G2 form,- together with theresistances m22m25, a device for supplying the calling subscribers linewith constant current.

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The electron tube E23, together with the resistances m215-m223, forms aWave shaper connected between the two amplifying tubes E22 and E24. Thetransformer T2 is an output transformer for adapting the tube E24 to itsload, which consists of the resistance m227 and the filters F1-F11 inFig. 3.

In Fig. 3, Fl-Fll are filters for eleven (11) different frequencies, ofwhich F1-F10 correspond to the push buttons Pl Plll in Fig. 1. Thefrequency F11 is developed by the generator E1 in the subscribersinstrument, when the push button K alone is pressed down and themicrotelephone is not lifted. The combined filters Fl-F 10 are over therectifiers e1--e5, and others, connected to the discharge lamps 631-642.A relay R11R22 is connected to each discharge lamp. Four (4) dischargelamps with associated relays are used for each figure which is to beregistered.

The relays R1R5 shift the different groups of dis charge lamps G31G24,635-638 and (139-642, as the figures arrive to the register. Relay R7 isa current feeding relay, which holds the connection between the callingsubscriber and the register during dialing and establishing of theconnection.

A call from the subscribers instrument in Fig. 1 starts when the pushbutton K is pressed down, after which it is locked by the spring 17. Thecontact 15 is closed and the contact 16 is broken. The line circuit isclosed over the contact 15, the right winding on transformer T12,resistance m12, the filament in the electron tube E1, with the parallelresistance m14, the right winding on transformer T13 and resistancer1113. A line relay at the telephone exchange starts a line finder SaSc,which tests the cut off relay BR of the calling line. The test relay SR3attracts its armature. The contacts 231-234 are closed. The registerfinder Va--Vc selects a free register, after which relay SR1 attractsits armature and the contacts 211-213 are closed.

The following circuit is closed, ground Fig. 2, contact wiper Vb,contacts 212, 221 and 231, contact wiper Sa, conductor a, contact 15 inFig. 1, T12, m12, and filament of E1, T13, m13, conductor b, contactwiper Sb in Fig. 2, contacts 232, 223, 211, contact wiper Va, conductort1, resistance m20 in Fig. 3, relay R7, conductor t2, electron tube E21in Fig. 2, resistance m24, to 220 volts.

The electron tube E1 in Fig. l is actuated by said circuit. The filamentis heated, the screen grid is energized over the resistance mill and theanode is energized through transformer T12. The control grid isenergized with help of suitable current over the left winding ontransformer T13 through the voltage drop in resistance m13. The leftwinding on transformer T13 forms together With the condenser C14 anoscillating circuit, the frequency of which corresponds with theresonance frequency for the filter P11 in Fig. 3. Through thetransformer T13, the oscillations in the oscillating circuit T13-C14actuate the electron tube E1, which begins to oscillate and emits a tonefrequency current through the transformer T12, the primary side of whichis closed through the condenser C12. The voltage on the screen grid isthereby kept relatively constant by means of the condenser C13.

In order that the electron tube E1 with resistances m11m14 may functionindependently of the resistance of the subscribers line, the energizingcurrent from the telephone exchange is kept constant by means of theelectron tube E21 in Fig. 2. The voltage of the screen grid is keptconstant with relation to the cathode of the tube by means of thedischarge lamp G2, which is energized through a series circuit includingthe resistances m24 and m25. The voltage of the control grid of theelectron tube B21 is kept constant by means of the resistances m22 andm23. When the anode circuit is closed, a current is obtained through thetube E21 and a change arises in the initial voltage of the control gridthrough increased voltage drop over resistance m24. The electron tubeE21 is thereby automatically set on a fixed current independently of theresistance of the connected subscribers line. The resistance m24 isadjustable so that the value of the anode current may be adjusted.

The energizing current over the subscribers line actuates relay R7 inFig. 3. The contacts 371-372 are closed. Relay R7 is slow operatingowing to the resistances m20 and m21 and the condenser C31, wherebyrelay R6 has time to attract and actuates the contacts 361362 beforecontact 372 is closed. Relay R6 is actuated by the tone frequencycurrent, the frequency of which is determined by condenser C14 in Fig. 1and is allowed to pass through filter F11. The contacts 361362 areactuated.

The a. c. generated by the electron tube E1 in Fig. 1 passes thecondenser C21 and the resistance 171213 in Fig. 2. The voltage overresistance m213 actuates the control grid of the amplifying tube E22,the screen-grid voltage of which is determined by the resistances 111226and m216218. The resistance 111212 and the condenser C23 keep thevoltage of the screen-grid constant. The amplified a. 0. passes overcondenser C22 and resistance 111215 to the above mentioned trigger.

The trigger consists of a double tube E23 with resistances m219m223. Atrest the left half of the tube E23 is energized and the voltage dropover resistance m220 produces a negative voltage on the control grid forthe right half. If a voltage wave comes in over condenser C22 andresistance m215, one of its half waves will produce a change of thecurrent through the tube E23 from the left half to the right half, sothat the voltage drop over resistance m219, together with the voltagedrop over resistance m220, produces on the control grid in the left halfof the tube a negative voltage. When the current in the left half of thetube decreases, the voltage drop over the resistance m220 decreases, andthe voltage on the right control grid increases. The current throughresistance m221 suddenly ceases.

The current through the resistance m221 decreases and the voltage changeon the condenser C24 actuates the control grid in the amplifying tubeE24, the screen grid of which is energized over resistance M1226 and iskept constant by means of an electrolytic condenser C25. A rectangularcurrent wave is obtained through the tube E24, the resistance 111225 andthe transformer T2. The transformer T2 is matched to the filters F1-F11and the load resistance 111227. The electron tubes E22E24 are energizedwith anode current from a battery with an electromotive force of 250volts.

The transformer T2 in Fig. 2 is connected through the conductors t3t4 tothe filters F1-F11 in Fig. 3. Each filter comprises a transformer, twocondensers, a coil and a load resistance, which are connected as isshown for filter F1 in Fig. 3. As stated above, the filter F11 isresonated for the frequency determined by condenser C14 and transformerT13 in Fig. 1. Each one of the filters F1-F10 allows one of the tenfrequencies to pass, these being developed by connecting the condenserC15 by means of one of the push buttons P1-P10 to different terminals onthe left winding of transformer T13.

The emitted frequency changes for each figure selected by the set ofpush buttons Pl-P10, and thus relay R6 releases its armature;simultaneously, a voltage arises over one of the resistances m4lm4=4,whereby the corresponding discharge lamps G31G42 glow. Assuming that thepush button P1 is pressed down, voltage arises over resistance 11141.The transformer in filter F1 is energized through the resonance filterF1. One of the half waves passes the rectifier el and the resistance m31and the other one passes the rectifier e2 and the resistance m41. Thevoltage over resistance 11141 is added to a voltage of 65 volts on thedischarge lamp G31, which then glows. Relay R11 attracts its armaturethrough the following circuit; +150 volts, contact 371, winding on relayR11, discharge lamp G31, contact 311 to which is at ground potential.The contact 301, and other contacts for registering operated by relayR11 (which are not shown on the figure), are actuated. Relay R11 holdsitself with an auxiliary voltage of +100 volts. Simultaneously, twocircuits are closed, one from contact 361 through the upper winding ofrelay R5 over contact 351 and one over contact 341 through the lowerwinding of relay R5 to contact 372. The two windings of relay R5counteract each other, and therefore the said two circuits do notactuate relay R5. When contact 341 breaks and 342 closes, no otherchange takes place than that the lower winding is energized from contact342 instead of over contacts 361 and 341. When the signal ceases, thetone frequency which actuates relay R6 resumes. Contact 361 breaks andcontact 362 010565. The

current through the upper winding on relay R5 is thereby broken, but notthe current through its lower winding, and therefore relay R5 attractsits armature. The contacts 3513S2 are actuated. Simultaneously thefollowing circuit is closed; contacts 362, 343 and 315, winding on relayR1, contact 372 to negative. Relay R1 attracts its armature. Thecontacts 311-315 are actuated. Relay R1 is thereafter kept energizedover contact 314.

On the following signal relay R6 releases its armature again. The lowerwinding on relay R4 is energized over the contacts 361, 352 and 372.Since the two Windings on relay R4 counteract each other, relay R4releases its armature. Relay RS on the other hand is kept energizedthrough its lower winding until the end of the signal and relay R6attracts its armature, whereby the current is broken by contact 361.Relay R5 releases its armature. The following circuit is closed;contacts 362, 344 and 325, winding on relay R2, contacts 313 and 372 tonegative. Relay R2 attracts its armature. Contacts 321-325 are actuated.Relay R2 is kept energized over contact 324.

Assume now that the push button P10 in the subscribers instrument, Fig.1, was pressed during the above mentioned second signal. The tonefrequency for which the filter P10 is resonated, is emitted from thesubscribers instrument. One of the half waves of the alternating voltagearising in the secondary winding on the transformer in filter F10produces a rectified current through the rectifier e5 and the resistancem30. The other half wave causes rectified currents through therectifiers c3 and 64 and the resistances m41 and m43. The voltage dropsacross resistances 21141 and m43 are added to the voltage of +65 voltsand the discharge lamps G35 and G37 glow in the following circuit;contacts 312 and 321, discharge lamps G35 and G37 winding on relays R15and R17, contact 371 to volts. Relays R15 and R17 attract theirarmatures and are held across contacts 302 and 303. Simultaneously othercontacts of the relays G35 and G37 are also closed (which contacts arenot shown on the drawing, since they are now essential to theinvention). The combination G35 and G37 indicates the figurecorresponding to the signal.

According to the invention, a third figure can also be indicated in theregister after relay R2 has attracted its armature. One or two of thedischarge lamps G39-G42 thereby glow and the corresponding relaysR19-R22 attract their armatures. At the end of the signal relay R3attracts. Contact 331 breaks the current through the discharge lamps anda circuit is closed over contacts 312, 322 and 332 and wire t5 actuatingparts of the register, which are not drawn on the figure, whereby anindication is given, that three figures have been received.

The register REG thereafter arranges a communication and is released bybeing connected to wire t6 in Fig. 2, whereby a circuit for relay SR2 isclosed over the contact wiper Vc and contact 213. Relay SR2 attracts itsarmature and the contacts 221-226 are actuated. The current for relaySR1 is broken by contact 226. Relay SR1 releases its armature and theregister is released. Relay SR2 is kept energized over contacts 225 and233. A communication is established between the wires ab and the wiresa1-b1.

Instead of rectifiers and discharge tubes it is of course possible touse different transformers in each one of the filters F5-F10 to selectthe receiving relays R11R14 which are actuated by the same filter.

According to the description above the tone frequency currents receivedby the filters have a constant amplitude and a determined wave shape,whereby it becomes possible to avoid disturbances caused by harmonics.The wave shaper in Fig. 2 gives a rectangular voltage wave with markedharmonics. These are however determined as to their frequency andamplitude, and therefore it is possible to prevent disturbing effects.This can be done by selecting the eleven frequencies, which are used forsignal emission, so that by means of well tuned filters they can becertainly distinguished from the disturbing harmonies.

Another way of preventing disturbances from harmonies is to select theeleven frequencies so that the high frequencies act as harmonics withrespect to rectangular waves of some of the low frequencies and toconnect a filter for a low frequency with a filter for a high frequency,the latter being a harmonic for the low frequency, and let the frequencycombination represent a signal. This method has been used in the abovedescribed embodiment and will be more clearly illustrated below with theaid of an example. In the table below the frequencies for which thefilters F1F10 are resonated are indicated in relation to those of thedischarge lamps G31-G34, which glow at the first figure, and to thefigures lcorresponding to the push buttons P1-P10 in Fig. 1.

It appears from the above table that the filter F5 allows the frequency1060 cycles per sec. to pass, the second hamonic of which is about 2000cycles per sec. and passes the filter F1. To prevent disturbances, thefilter F5 is connected across the rectifier e6 to the discharge lampG31, as well as the filter F1, and the combination of the dischargelamps G31 and G32 corresponds to the figure 5. The filter F8 isresonated for 670 cycles per sec., the third harmonic of which is about2000 cycles per sec., and therefore F8 is connected as well to G31 as toG34 and the combination G31+G34 corresponds to the figure 8.

We claim:

1. In an automatic telephone system, a line circuit," at least onesending station including a sender and at least one receiving stationincluding a receiver therein, a voice frequency generator in said senderfor transmitting voice frequency currents and a key set in said senderconnected to said voice frequency generator for controlling thefrequency of the currents transmitted by the sender over the linecircuit to the receiver, a plurality of band pass filters in saidreceiver tuned respectively to the currents generated by said generator,and a plurality of designating circuits connected to said filters to beenergized by the respective currents, the frequency of at least one ofsaid currents being substantially a harmonic with respect to thefundamental frequency of another of said currents, the band pass filterfor said harmonic being connected to only one of said designatingcircuits, and the band pass filter for said another of said currentsbeing connected both to the last-named designating circuit and to atleast one other of said circuits for designating another signal throughthe combination of the said latter two circuits.

2. In an automatic telephone system, a line circuit, at least onesending station including a sender and at least one receiving stationincluding a receiver, a voice frequency generator in said sender fortransmitting voice frequency currents and a key set connected to saidvoice frequency generator for controlling and selecting the frequency ofthe currents transmitted by the sender over the line circuit to thereceiver, a wave shaper in said receiver connected to the incoming endof the line circuit for transforming incoming alternating voltage wavesfrom said line circuit into alternating voltage waves of predeterminedshape and constant amplitude having the same fundamental frequency asthe incoming waves, said receiver also including a plurality of bandpass filters connected to said wave shaper and individually tuned to thefrequencies produced by said generator, and a plurality of circuitsconnected to said filters to be energized by the respective currents,the frequency of at least one of said currents being an harmonic withrespect to the fundamental frequency of another of said currents, theband pass filter tuned to said harmonic being connected to only one ofsaid circuits for designating a signal, and the band pass filter tunedto said fundamental frequency being connected both to said one circuitand to at least one other of said circuits, for designating anothersignal through the energization of the combination of said two circuits.

3. In an automatic telephone system, a line circuit, at least onesending station including a sender and at least one receiving stationincluding a receiver, said sender including a switch and a tonefrequency generator which emits tone frequency current having afundamental frequency which indicates a signal and which frequency isdetermined by the position of said switch, in said receiver at least oneregistering device consisting of relays connected to be energized incombinations, and filters connected thereto, and a wave shaper connectedahead of said filters for transforming incoming alternating waves ofarbitrary shapes and amplitudes into wave shapes of predetermined formsand constant ampiltude with the same fundamental frequency as theincoming alternating wave, at least one of said filters tuned to pass alow frequency signal being connected to more than one registering relayin said registering device, whereby signals passed by said filter areindicated by more than one simultaneously actuated registering relay,and another of said filters tuned to pass higher frequency signals beingconnected to only a single registering relay in said registering device,said higher frequency being harmonic with respect to the fundamentalfrequency of said low frequency signal, and one of said registeringrelays connected to said one of said filters being connected to thefilter which passes said harmonic.

4. In an automatic telephone system in accordance with claim 1, a firstand a second registering device in said receiver, each consisting ofrelays which are energized in combinations, means including a switch inthe sending station for tuning said tone frequency generator to apredetermined frequency when said switch is in its rest position, andfor changing said certain frequency to a signaling frequency whenoperated and restoring said predetermined frequency upon return to itsrest position, controlling means in said receiver responsive to saidpredetermined frequency and a relay device operated by said controllingmeans for disconnecting said first and connecting said secondregistering device to said filters when said switch is operated andreturns to its rest position.

References Cited in the file of this patent UNITED STATES PATENTS

